16-04: Hydrolysis of steam-treated sugarcane bagasse at high total solids and low enzyme loadings

Enzymatic hydrolysis of biomass is an important alternative to the growing demand for liquid fuels. However, some challenges must be overcome such as enzyme cost, mass transfer limitations, end-product inhibition and unproductive/irreversible adsorption, especially when using lignified substrates in high solid concentrations. The main objective of this work was to produce high concentrations of fermentable sugars using enzymatic hydrolysis at high substrate consistencies. Experiments were carried out for 72h at 50ºC using Cellic Ctec 2 (Novozymes) and phosphoric-acid impregnated steam-treated cane bagasse, with the reaction conversions always being monitored by HPLC. All experiments were organized in a 2³ factorial design using the following variables in two levels: enzyme concentration (0.1 and 0.025 g.g^-1 cellulose), substrate consistency (5 and 20 wt%) and agitation intensity (150 and 200 rpm). The highest conversion of 88.1% (26,6g.L^-1) was obtained with 0.1g of enzyme/g of cellulose, 5 wt% total solids and 200 rpm. However, the highest amount of fermentable sugars (82.7g.L^-1, corresponding to a cellulose conversion of 65.5 wt%) was derived from experiments carried out at 20 wt% total solids. Hence, the enzymes of the Cellic CTec 2 family were able to produce high saccharification levels of lignified cellulosic substrates under high total solids and relatively low enzyme loadings, showing a performance by far superior to that obtained with the same loading of the Celluclast 1.5L / Novozym 188 enzyme mixture. Also, the results of the factorial design were statistically valid and a good correlation was observed between the mathematical model and the experimental data.